I have seen some people mention changing saddle height between inside and outside. May be fine and beneficial, but I will say that a change of 20mm that you mention seems rather large (even extreme?) to me.
- Per my other comments on saddle comfort (2nd half of item #3), I personally feel that dead level setups inside are not ideal. It may work for many people, but I find that lifting the front a bit can help with hand and saddle comfort.
The next consideration for me would be related to your specific trainer in use, trainer mode, gearing, cadence and your similar use outside. Identify any/all differences present in your trainer vs outside and consider their potential impact on your body.
Obviously, pictures and video of you inside and even outside might be beneficial in diagnosing the things you may not know to look for or be able to identify as you ride. Could be worth a fitting session but we can see if there’s something to be done remotely.
- Yeah, no surprise that I consider rigid trainer setups a less than perfect solution. There are small and large ways to add motion, but it seems beneficial in the majority of cases I have seen. Some still prefer fixed even after trying motion, and that’s fine. But there is just so much different when you lock a bike in position that is free to float, lean and wiggle when outside.